1. Field of the Invention
The present invention relates to an RF switch matrix circuit and driving method thereof, and more particularly, to a loading-adjustable RF switch matrix circuit and driving method thereof.
2. Description of the Prior Art
Due to the rapid development of wireless communication systems, wireless devices offering great convenience are widely used in daily communications. With wireless devices, people are able to exchange information, share experiences, and communicate with each other anytime and anywhere. Because of the wide usage of wireless devices, a broad range of new wireless products are being developed. As indicated by Brunner, et al. in U.S. Pat. No. 5,754,118, an RF switch matrix is applied to wireless communication such as digital satellite broadcasting (DSB) and digital video broadcasting (DVB).
Please refer to FIG. 1. FIG. 1 is a schematic diagram of a prior art RF switch matrix circuit. The RF switch matrix circuit 100 is a 4×2 RF switch matrix circuit comprising: a plurality of switches 100a; a plurality of input nodes IN-A, IN-B, IN-C and IN-D; and a plurality of output nodes OUT-1 and OUT-2. A plurality of RF signals RFa, RFb, RFc, and RFd are inputted into the input nodes IN-A, IN-B, IN-C and IN-D respectively, and then chosen by the plurality of switches 100a. The RF signal RF1 of output node OUT-1 could be one of the RF signals RFa, RFb, RFc, or RFd. The other RF signal RF2 of output node OUT-2 could be one of the RF signals RFa, RFb, RFc, or RFd. Generally speaking, the output nodes OUT-1 or OUT-2 in the RF switch matrix circuit 100 can further be coupled to the outside set-top box (STB) through outside amplifiers.
For the RF switch matrix circuit 100, the STB can be taken as a loading resistance having a specific impedance such as 75 ohms. When one of the output nodes OUT-1 or OUT-2 does not couple to the outside STB, the output loading of the RF switch matrix circuit 100 will change. This change of output loading will further affect the plurality of switches 100a inside the RF switch matrix circuit 100, and finally cause bad isolation between the plurality of switches 100a. For example, if the plurality of switches 100a choose RF signals RFa and RFd to become output signals through proper control and a user does not connect an STB to the output node OUT-1, the RF signal RFa will couple to output node OUT-2 through switches 100a inside the RF switch matrix circuit 100, and therefore interfere with the RF signal RFd of output node OUT-2.